Sailboat block with shackle adapter

ABSTRACT

A sailboat block having a swivel shackle, and an adapter for holding the shackle non-rotatably in different angular positions, as a front shackle, a side shackle, or a diagonal shackle. The adapter comprises a collar which telescopes over the shackle fitting of the block, and two locking fingers on the collar which project into the structure of the block which supports the sheave, and prevent rotation of the collar, and thus of the shackle, relative to the sheave. In one form the collar is simply rectangular, and in another form it has internal notches in its sidewalls.

United States Patent [1 1 Holmes NOV. 20, 1973 SAILBOAT BLOCK WITH SHACKLE ADAPTER [75] Inventor: Tracy S. Holmes, Santa Monica,

Calif.

[73] Assignee: Tracy Holmes Corporation, Santa Monica, Calif.

[22] Filed: July 31, 1972 [21] Appl. No.: 276,562

[52] US. Cl. 254/195 [58] Field of Search ..254/l90l96; 248/11 [56] References Cited UNITED STATES PATENTS 2,291,894 8/1942 Owinn 254/195 FOREIGN PATENTS OR APPLICATIONS 161,189 6/1918 Great Britain 254/192 Primary Examiner-Richard A. Schacher AttorneyThomas MI Small et a1.

[5 7] ABSTRACT A sailboat block having a swivel shackle, and an adapter for holding the shackle non-rotatably in different angular positions, as a front shackle, a side shackle, or a diagonal shackle. The adapter comprises a collar which telescopes over the shackle fitting of the block, and two locking fingers on the collar which project into the structure of the block which supports the sheave, and prevent rotation of the collar, and thus of the shackle, relative to the sheave. In one form the collar is simply rectangular, and in another form it has internal'notches in its sidewalls.

14 Claims, 10 Drawing Figures SAILBOAT BLOCK WITH SHACKLE ADAPTER BACKGROUND OF THE INVENTION This invention relates to boat hardware, and more particularly to the pulleys, known as blocks, which are used in the running rigging of small sailboats to gain mechanical advantage and to change the direction of lines.

Such blocks are provided in various sizes, and with different mounting structures and fittings. Basically, each block comprises a grooved roller, or sheave, that is rotatably mounted between two spaced side plates, or cheeks, on an axle that is carried by the checks. The latter are secured together to form a shell, and a shackle is attached to the shell at one end for use in securing the block to a supporting part such as a mast, boom, or deck surface, with a suitable fastening such as an eye or an eye strap.

To secure the shackle to the block, a shackle mount is provided on one peripheral side of the shell, for example, by a U-shaped strap between which the plates are supported, or by a spacer extending between and reveted to the plates, and a shackle fitting projects outwardly from the mount for connection to the shackle. The typical shackle is a clevis, a U-shaped piece of metal or the like having two legs which straddle the shackle fitting and are releasably connected thereto by a pin extending through aligned holes in the legs and through the fitting. The shackle fitting braces the shackle in use, by holding the legs of the shackle apart when tension is applied to the block.

Since lines pass through blocks from various angles, blocks have been provided with shackles that are fixed at different angles relative to the sheave, typically as side shackles in which the opening through the shackle is in the same direction as the opening between the plates, and as front shackles in which the opening is parallel to the axis of the sheave. The shackles may be fixed in these positions by tightly riveting the fitting to the mount with the fitting in the desired position. There also are swivel shackle blocks in which the shackles are free to turn into any angular position relative to the sheave, the rivets of these blocks being loose.

To meet the demand for the various types of blocks, it has been necessary to manufacture and stock the three types of blocks in each of the various sizes and designs that might be needed. This has resulted in considerable expense in manufacture, inventory and related matters.

SUMMARY OF THE INVENTION The present invention resides in a novel, simple and inexpensive adapter for use with a block of the swivelshackle type to hold the shackle selectively in different angular positions relative to the sheave, so that one type of block can be manufactured, stocked, sold and used to serve all of the difierent functions. The adapter fits around the shackle fitting of the block, and cooperates with the shackle mount in fixing the shackle in a desired position, either as a front shackle or as a side shackle, and also permits the block to be readily converted from one type to another. Moreover, the adapter may be removed to permit the block to function as a swivel-shackle block, and usually can be stored in an idle position on the block for eventual use in converting back to the frontor sideshackle configuration.

More secifically, and as illustrated in the preferred embodiments shown herein, the adapter comprises a collar having a through opening of non-circular crosssection, for telescoping over the shackle fitting of a swivel-shackle block with a close fit in each of the desired angular positions of the block, and having abutment means thereon for engaging the fixed shackle mount of the block and preventing turning of the collar relative to the sheave. The adapter normally is retained on the fitting by the shackle itself, and can be removed when the shacked is disconnected, to permit the fitting to be turned to a new angular position. Then, when the adapter is replaced, it holds the fitting in the new position.

For use with conventional blocks in which the shackle fitting is substantially square in cross-section, the collar is simply an open-ended, box-like molding of rigid plastic having two integral and parallel locking fingers projecting in the same direction from opposite sides of the collar for engagement with parallel side edges of the shackle mount between the side plates. The fingers are rectangular tabs narrower than the sides of the collar and long enough to extend beyond the swivel joint and over the edges of the mount.

In one form of the invention, internal notches are formed in at least two sides of the collar, and preferably in all four sides, to provide clearance for a rivet head tha projects laterally from one side of some shackle fittings. These notches also permit the adapter to be placed around the fitting when the latter is in a diagonal position, that is, a position turned forty-five degrees from the front-shackle and side-shackle positions.

The outer edge surfaces of the collar abut against the outer end of the shackle mount when the adapter is placed around the shackle fitting in an inverted, storage position, with the locking fingers projecting idly outwardly, thus permitting the adapter to be stored on the block when the latter is to be used with a swivel shackle. The shackle also retains the adapter removably in this condition.

Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view, partly in cross-section, of a mainsheet rig illustrating the use of several blocks equipped with adapters in accordance with the present invention and shown in different illustrative positions;

FIG. 2 is an enlarged fragmentary perspective view of one of the blocks of FIG. 1, taken in the direction of the arrow 2, with the shackle thereof arranged as a front shackle;

FIG. 3 is an exploded perspective view of the block of FIG. 2;

FIG. 4 is a fragmentary perspective view, partly in cross-section, of another block of FIG. 1, with the shackle arranged as a side shackle;

FIG. 5 is an enlarged perspective view of the adapter alone;

FIG. 6 is an enlarged perspective view of another type of block that is equipped with an adapter of a modified type, holding the shackle in the side-shackle position;

agonal position; and

FIG. is an exploded perspective view of the parts shown in FIG. 7.

DETAILED DESCRIPTION As shown in the drawings for purposes of illustration, the invention is embodied in an adapter 10 for use in combination with sailboat blocks of the type indicated generally at 11, 12, 13 and 14 in the rigging of a sailboat 15. The illustrative rigging is a mainsheet rig in which a line 17 passes through the block 11 secured to one side of a boom 18, extends downwardly and through the block 12, which is secured to the deck. Then the line extends upwardly and through the block 13, which is secured to the other side of the boom, extends downwardly and through the block 14, and finally returns to the block 13 and is secured to a becket 19, a fitting on the lower side of the block. It is to be understood that this is only one of many rigs in which blocks are used, and that a variety of conventional fasteners may be used to secure the blocks in place.

In general, each block comprises a sheave 20 in the form of a peripherally grooved roller that is disposed in a shell formed by two cheeks 21, usually oval in shape, and is rotatably supported on an axle formed by a rivet 22 which usually carries an anti-friction bearing (not shown) so that the sheave will turn freely under load. The ends of this axle are shown in FIGS. l-4 as projecting through and riveted over two metal straps 23 on opposite sides of the block, thereby serving to hold the cheeks 21 in properly spaced relation, and a similar rivet 24 connects the opposite ends of the straps adjacent one peripheral edge of the shell. A spacer 25 telescoped onto this rivet between the cheeks cooperates in positioning the cheeks.

Projecting outwardly from the spacer 25 is a shackle mount 27 (FIG. 3) which, in this instance, is a U- shaped metal plate having two legs which extend in between the cheeks and are rigidly secured thereto by the rivet 24, the spacer being clamped between the legs. A shackle fitting 28, also a U-shaped metal plate, is swivelly connected to the mount by means of a rivet 29 loosely disposed in aligned holes in the crosspieces of the two plates with the legs of the shackle fitting projecting further outwardly and having a roller spacer 30 between their outer end portions and a passage 31 through the spacer aligned with holes in the legs.

A shackle 32 in the form of a U-shaped metal strap is releasably secured to the shackle fitting 28 by means of a pin 33 which is inserted through holes 34 in the ends of the legs of the shackle, and through the holes in the fitting and the passage 31 through spacer 30. A retainer 35, such as a cotter pin (not shown) or a coiled wire ring, is inserted through a hole in one end of the pin 33 to cooperate with a head on the other end of the pin in holding the pin in place.

The foregoing description is applicable to a conventional block of the swivel type, that is, in which the fitting 28 turns freely relative to the mount 27 to permit the sheave 20 to turn into any angular position to which it is urged by the line 17. In addition to this type of block, it has been necessary to provide both side shackles and front shackles, in which the shackle fitting is fixed in a selected angular position, typically by tightly riveting the fitting to the mount, so that the sheave will be positively held in a proper angular position relative to the shackle.

In accordance with the present invention, the adapter 10 is designed to fit around the shackle fitting 28 and to engage the supporting structure for the sheave 20 in difierent selected angular positions of the fitting relative to the shacke mount, and to lock the fitting in each angular position, thereby converting a swivel shackle selectively into a front shackle or a side shackle. Thus, the need for a number of different shackle arrangements for a given type of block is eliminated. Each type of block can be supplied with a swivel shackle and an adapter and then tailored to the specific use intended. If the use calls for a swivel shackle, the adapter can be omitted, or in some instances can be stored in an idle position on the block.-

For these purposes, the adapter 10 shown in FIGS. l-S may be a one-piece molding, preferably of rigid plastic such as that sold under the trademark Delrin, and comprises a box-like, open-ended collar 37 defining a through opening 38 (FIG. 5) of non-circular cross-section for telescoping closely and non-rotatably around the shackle fitting 28, and abutment means on the collar for engaging the shackle mount 27 when the adapter is in place, and preventing rotation of the collar, and thus of the shackle fitting, relative to the mount and the sheave 20. The shackle fitting customarily is square in transverse cross-section, and the opening 38 therefore also is square in cross-section, and only slightly larger than the fitting.

The preferred abutment means are two locking fingers 39, which may be parallel, rectangular tabs extending in the same direction from two opposite sidewalls of the collar 37 to lie along the two laterally facing, U-shaped side edges 40 (FIG. 3) of the shackle mount 27. These edges are flush with the sides of the shackle fitting when the latter is positioned for use as a front shackle and as a side shackle, so the locking fingers may be co-planar extensions of the two sidewalls of the collar from which they extend. The fingers are narrower than the sidewalls of the collar, however, so as to fit within the space between the cheeks 21, which thus cooperate with the side edges 40 in preventing rotation of the adapter 10.

As shown in FIGS. 2 and 3, the shackle fitting 28 may be positioned to receive the shackle 32 with the legs thereof lying on the sides toward which the open sides of the shell face, and with the opening through the shackle facing in the same directions as the flat sides of the cheeks. This is for a front shackle. The adapter may be telescoped over the shackle fitting when the shackle is removed, and positioned as shown in FIG. 2 with the locking fingers 39 inserted between the cheeks 21 and engaging the side edges 40 of the shackle mount 27. When the shackle then is secured to the fitting, it serves as a retainer for the adapter, the width of the collar opening 38 being less than the width of the adjacent end of the shackle. Thus, the edge surfaces of the outer end 41 of the adapter constitute retaining abutments engageable with the shackle when the latter is in place.

To change to a side shackle, as shown in FIG. 4, the shackle 32 is removed, the adapter is lifted away from the mount 27 at least far enough for the fingers 39 to clear the mount, and the fitting 28 is turned ninety degrees. Then the adapter is shifted back toward the mount until the fingers again overlie the edges 40. In the form shown in FIGS. 1-5, the fingers wedge in between the cheeks 21, which limit inward movement of the adapter. After the adapter has been returned to its locking position, the shackle is secured to the fitting and the block is ready for use.

With reference to FIGS. 6-10, it will be seen that the block 42 shown therein differs from the foregoing blocks in that the straps 43 on the outer sides of the cheeks 44 are the opposite end portions of a U-shaped bar straddling the cheeks and having a crosspiece 45 which extends across one peripheral side of the cheek, forming the shackle mount. A spacer is formed by two abutting lugs 47 formed on the inner sides of the cheeks adjacent the mount.

Here, the shackle fitting 48 is a metal block which is square in transverse cross-section, and is swivelly connected to the mount 45 by means of a screw 49 (see FIG. 10) that extends upwardly through the mount and is threaded into the underside of the fitting. A locking pin 50 preferably is pressed into the fitting to abut against the screw and lock it in place, and a crossbore 51 is formed in the fitting to receive a pin 52 for holding the shackle 53 releasably in place on the fitting. In this instance, the shackle pin 52 is threaded into one leg of the shackle to secure it in place.

A slightly modified adapter 54 is used for this type of block, to provide clearance for the head 55 of the lock ing pin 50 as shown in FIG. 7, and also to permit arrangement of the shackle 53 in a diagonal position, as shown in FIG. 9. Specifically, notches 57 are formed in all four walls of the through opening 58 (FIG. 10), the

notches being narrower than the width of the walls but at least as wide as the locking-pin head 55, and deep enough to receive either the head or, as shown in FIG. 9, two opposite corners of the fitting 48 when it is diagonally disposed.

When this adapter 54 is in its normal operative position, shown in FIGS. 6 and 7, the locking fingers 59 thereon project into the space between the cheeks 44 and terminate adjacent the spacer lugs 47. The cheeks thus may cooperate with the side edges 60 of the mount 45 in preventing turning of the adapter.

In this instance, the mount 45 is of elongated rectangular cross-section rather than square as in FIGS. 1-4, the narrower dimension being across the edges 60. Accordingly, when the adapter is placed over the fitting 48 in the inverted condition shown in FIG. 8, with the edge surfaces of the end 61 of the collar slidably engaging the mount and the locking fingers 59 projecting idly outwardly alongside the fitting, the shackle 53 is free to swivel as indicated by the arcuate arrow 62 in FIG. 8. This provides for storage of the adapter on a swivel shackle, for later use in conversion to a shackle of another type.

From the foregoing, it will be seen that the present invention provides a very simple and inexpensive adapter with which a swivel shackle may be converted selectively to a front shackle or a side shackle, or even to a diagonal shackle, if desired. This makes it possible to manufacture blocks with a single type of shackle for all uses, and to readily convert the block to any desired type in a rapid and simple operation. In effect, the invention provides a universal shackle.

It also will be apparent that, while specific embodiments of the invention have been illustrated and described, modifications and changes may be made without departing fron the spirit and scope of the invention.

I claim:

1. In combination with a sailboat block having a rotary sheave and a supporting structure for said sheave including two spaced plates straddling and rotatably supporting said sheave, a shackle mount secured to said plates and having edges extending across the space between the plates on one peripheral side of the sheave, a shackle fitting of substantially square transverse cross-section projecting outwardly from said mount, a swivel connection between said mount and said fitting, a shackle straddling said fitting, and a pin extending through said shackle and said fitting to hold the shackle releasably on the fitting;

an adapter for use in selectively holding said shackle in different angular positions relative to said sheave, comprising:

a collar of substantially square transverse crosssection composed of rigid material and defining a through opening of substantially square crosssection sized to fit closely around said fitting in a predetermined relation with said mount when the shackle is in said different angular positions;

said collar having edge surfaces facing outwardly in opposed relation with the adjacent portion of said shackle to abut against the latter and prevent removal of the collar when the shackle is in place;

and two flat locking fingers on said collar extending inwardly from opposite sides thereof to lie along and abut against said edges of said mount, thereby to prevent turning of said collar, and thus of said fitting, relative to said sheave, when said collar is in place;

said collar being removable from said fitting when said shackle is disconnected, to permit turning of said fitting to a new angular position to be maintained when said collar is replaced on said fitting.

2. The combination defined in claim 1 in which said collar comprises an open-ended, box-like structure defined by four rigid and integral sidewalls, and said fingers are formed integrally with two of said sidewalls to extend inwardly in common planes with said two sidewalls.

3. The combination defined in claim 2 in which said collar has a notch in each inside wall forming one side of said through opening sized and positioned to receive a comer of said mount when the latter is in a diagonal position relative to the collar and the block, and to hold said mount and the shackle generally in said diagonal position.

4. The combination defined in claim 1 in which said mount has an elongated rectangular outer end, and said edges are spaced apart a preselected distance that is less than the spacing of said fingers, said outer end being longer than said preselected distance so as to abut against said edge surfaces when said collar is placed on said fitting in an inverted storage position with said fingers projecting outwardly and leaving said fitting free to swivel relative to said mount.

5. The combination defined in claim 1 in which said collar comprises a one-piece, open-ended, box-like structure of rigid plastic formed by four rigid sidewalls having inside surfaces for engaging said mount, said locking fingers constituting integral and co-planar extensions projecting in the same direction from the sidewalls constituting opposed sides of the collar, and being narrower than the length of such sidewalls so as to project into the space between the plates.

6. In combination with a sailboat block having a rotary sheave and a supporting structure for said sheave including two spaced plates straddling and rotatably supporting said sheave, a shackle mount secured to said plates and positioned on one peripheral side of the sheave, a shackle fitting of non-circular cross-section projecting outwardly from said mount, a swivel connection between said mount and said fitting, a shackle projecting further outwardly from said fitting, and means releasably connecting said shackle to said fitting;

an adapter for use in selectively holding said shackle in at least two different angular positions relative to said sheave, comprising:

a collar composed of rigid material and defining a through opening of non-circular cross-section sized and shaped to fit around said shackle fitting with a close fit, said collar being telescoped over and disposed around said fitting in a locking position adjacent said shackle mount, and said shackle being disposed in one of said angular positions;

said shackle fitting also receiving said collar in said locking position when the shackle fitting is in the other of said angular positions;

outwardly facing first abutment means on said collar for preventing removal of said collar when said shackle is connected to said fitting and permitting removal of the collar when said shackle is disconnected;

and second abutment means on said collar for preventing swivelling of said collar and said shackle relative to said sheave when said collar is in said locking position, whereby said adapter holds the shackle securely in a selected angular position, may be removed when said shackle is released from said shackle fitting to permit turning of the fitting to the other angular position, and may be repositioned on the shackle fitting to hold the latter securely in the new angular position.

7. The combination defined in claim 6 in which said shackle fitting and said through opening are: substantially square in cross-section.

8. The combination defined in claim 6 in which said first abutment means are edge surfaces on said collar in opposed relation with the adjacent end of said shackle when the latter is releasably connected to said shackle fitting.

9. The combination defined in claim 6 in which said second abutment means include at least one locking finger on said collar extending inwardly along said shackle mount.

10. The combination defined in claim 9 in which said shackle mount has laterally facing third abutment means between the planes of said side plates, and said finger engages said third abutment means.

1 l. The combination defined in claim 9 in which said collar is substantially square, and said second abutment means comprise two parallel locking fingers extending inwardly from two parallel sides of the collar closely adjacent opposite sides of the shackle mount.

12. The combination defined in claim 6 in which said through passage and said shackle fitting are substantially square in cross-section, said collar further having a notch in each inside wall forming one side of sair. through opening to receive said shackle fitting with the corners thereof in said notches and hold the shackle in a diagonal position.

13. The combination defined in claim 6 in which said shackle mount has outwardly facing fourth abutment means for engaging said first abutment means when said collar is telescoped onto said shackle fitting in an inverted condition, with said second abutment means disposed outwardly from said swivel connection, thereby permitting storage of said adapter on said supporting structure in an idle position in which the shackle is free to swivel relative to said sheave.

14. The combination of:

a sailboat block having supporting structure including a shackle mount on one side, and a swivel shackle of non-circular cross-section connected to and projecting outwardly from said mount;

and an adapter for holding said shackle in different predetermined angular positions relative to said mount, and having non-circular collar means for fitting non-rotatably around said swivel shackle in said different positions, and abutment means carried by said first collar means for engaging said supporting structure in said different positions and preventing substantial rotation of said collar means, and thus of said swivel shackle, relative to the supporting structure. 

1. In combination with a sailboat block having a rotary sheave and a supporting structure for said sheave including two spaced plates straddling and rotatably supporting said sheave, a shackle mount secured to said plates and having edges extending across the space between the plates on one peripheral side of the sheave, a shackle fitting of substantially square transverse cross-section projecting outwardly from said mount, a swivel connection between said mount and said fitting, a shackle straddling said fitting, and a pin extending through said shackle and said fitting to hold the shackle releasably on the fitting; an adapter for use in selectively holding said shackle in different angular positions relative to said sheave, comprising: a collar of substantially square transverse cross-section composed of rigid material and defining a through opening of substantially square cross-section sized to fit closely around said fitting in a predetermined relation with said mount when the shackle is in said different angular positions; said collar having edge surfaces facing outwardly in opposed relation with the adjacent portion of said shackle to abut against the latter and prevent removal of the collar when the shackle is in place; and two flat locking fingers on said collar extending inwardly from opposite sides thereof to lie along and abut against said edges of said mount, thereby to prevent turning of said collar, and thus of said fitting, relative to said sheave, when said collar is in place; said collar being removable from said fitting when said shackle is disconnected, to permit turning of said fitting to a new angular position to be maintained when said collar is rEplaced on said fitting.
 2. The combination defined in claim 1 in which said collar comprises an open-ended, box-like structure defined by four rigid and integral sidewalls, and said fingers are formed integrally with two of said sidewalls to extend inwardly in common planes with said two sidewalls.
 3. The combination defined in claim 2 in which said collar has a notch in each inside wall forming one side of said through opening sized and positioned to receive a corner of said mount when the latter is in a diagonal position relative to the collar and the block, and to hold said mount and the shackle generally in said diagonal position.
 4. The combination defined in claim 1 in which said mount has an elongated rectangular outer end, and said edges are spaced apart a preselected distance that is less than the spacing of said fingers, said outer end being longer than said preselected distance so as to abut against said edge surfaces when said collar is placed on said fitting in an inverted storage position with said fingers projecting outwardly and leaving said fitting free to swivel relative to said mount.
 5. The combination defined in claim 1 in which said collar comprises a one-piece, open-ended, box-like structure of rigid plastic formed by four rigid sidewalls having inside surfaces for engaging said mount, said locking fingers constituting integral and co-planar extensions projecting in the same direction from the sidewalls constituting opposed sides of the collar, and being narrower than the length of such sidewalls so as to project into the space between the plates.
 6. In combination with a sailboat block having a rotary sheave and a supporting structure for said sheave including two spaced plates straddling and rotatably supporting said sheave, a shackle mount secured to said plates and positioned on one peripheral side of the sheave, a shackle fitting of non-circular cross-section projecting outwardly from said mount, a swivel connection between said mount and said fitting, a shackle projecting further outwardly from said fitting, and means releasably connecting said shackle to said fitting; an adapter for use in selectively holding said shackle in at least two different angular positions relative to said sheave, comprising: a collar composed of rigid material and defining a through opening of non-circular cross-section sized and shaped to fit around said shackle fitting with a close fit, said collar being telescoped over and disposed around said fitting in a locking position adjacent said shackle mount, and said shackle being disposed in one of said angular positions; said shackle fitting also receiving said collar in said locking position when the shackle fitting is in the other of said angular positions; outwardly facing first abutment means on said collar for preventing removal of said collar when said shackle is connected to said fitting and permitting removal of the collar when said shackle is disconnected; and second abutment means on said collar for preventing swivelling of said collar and said shackle relative to said sheave when said collar is in said locking position, whereby said adapter holds the shackle securely in a selected angular position, may be removed when said shackle is released from said shackle fitting to permit turning of the fitting to the other angular position, and may be repositioned on the shackle fitting to hold the latter securely in the new angular position.
 7. The combination defined in claim 6 in which said shackle fitting and said through opening are substantially square in cross-section.
 8. The combination defined in claim 6 in which said first abutment means are edge surfaces on said collar in opposed relation with the adjacent end of said shackle when the latter is releasably connected to said shackle fitting.
 9. The combination defined in claim 6 in which said second abutment means include at least one locking finger on said collar extending inwardly along said shackle mount.
 10. The combination defined in claim 9 in which said shackle mount has laterally facing third abutment means between the planes of said side plates, and said finger engages said third abutment means.
 11. The combination defined in claim 9 in which said collar is substantially square, and said second abutment means comprise two parallel locking fingers extending inwardly from two parallel sides of the collar closely adjacent opposite sides of the shackle mount.
 12. The combination defined in claim 6 in which said through passage and said shackle fitting are substantially square in cross-section, said collar further having a notch in each inside wall forming one side of said through opening to receive said shackle fitting with the corners thereof in said notches and hold the shackle in a diagonal position.
 13. The combination defined in claim 6 in which said shackle mount has outwardly facing fourth abutment means for engaging said first abutment means when said collar is telescoped onto said shackle fitting in an inverted condition, with said second abutment means disposed outwardly from said swivel connection, thereby permitting storage of said adapter on said supporting structure in an idle position in which the shackle is free to swivel relative to said sheave.
 14. The combination of: a sailboat block having supporting structure including a shackle mount on one side, and a swivel shackle of non-circular cross-section connected to and projecting outwardly from said mount; and an adapter for holding said shackle in different predetermined angular positions relative to said mount, and having non-circular collar means for fitting non-rotatably around said swivel shackle in said different positions, and abutment means carried by said first collar means for engaging said supporting structure in said different positions and preventing substantial rotation of said collar means, and thus of said swivel shackle, relative to the supporting structure. 